1. Field of the Invention
This invention relates to a method of producing a semiconductor device or the like as well as a processing method of removing a photoresist on a substrate used for the method, a residue thereof, or the like and particularly, relates to a processing method of removing a residue which results from ion implantation of a dopant or the like and is difficult to ash (hereinafter simply referred to as xe2x80x9cnonashable residuexe2x80x9d).
2. Related Background Art
In the production process for a semiconductor device, a photoresist as a photosensitive resin is widely used as a masking material for selective etching and local ion implantation to form a device structure. The corresponding photoresist needs to be removed after various processes utilizing this, and in recent years, is generally removed by oxidization and ashing through dry processing with oxidation action mainly using oxygen plasma, oxygen radicals, ozone, and so on.
As a method of removing a photoresist as an organic substance consisting mainly of carbon and hydrogen, a technique is widely used in which the photoresist is exposed to oxygen as activated by electric discharge or irradiation with ultra violet and is gasified through the oxidation action into steam, carbon dioxide, carbon monoxide, etc., thus effecting ashing and removal.
On the other hand, in the case where a photoresist is used as a mask for ion implantation of a dopant, etc., the resist, the surface of which is modified by the energy of implanted ions, will be difficult to remove by oxidation, so that the processing efficiency decreases significantly. In addition, it is known that, when an ion implanted photoresist is heated to 150xc2x0 C. to 250xc2x0 C. as the normal ashing temperature, the phenomena (popping) that the surface modified layer bursts by steam of an organic solvent generated from an unmodified layer in a lower portion of the photoresist to form flake-shaped particles to be scattered around, is observed, so that the wafer is contaminated. Moreover, since dopant ions such as As, P, B, etc. do not form any substance of a high vapor pressure by oxidation, oxides of the ions will remain on the wafer after the resist has been ashed and removed by oxygen-based active species and needs to be removed by subsequent wet processing.
For the purpose of removing the above mentioned resist which is generated after ion implantation and is difficult to ash, there have hitherto been proposed a method in which after a modified layer of the resist surface is removed while hydrogenating and removing the dopant ions with a hydrogen plasma or steam plasma, an underlying unmodified layer is ashed and removed with an oxygen plasma, a method in which the resist is ashed and remove with a plasma of a mixed gas obtained by adding to oxygen gas a gas containing fluorine having a function to increase the ashing rate and to remove the implanted ion species, or the like.
In addition, Japanese Patent Application Laid-Open No. 5-275326 discloses a method in which after processing using oxygen and CF4, a further processing is effected using oxygen and nitrogen, and Japanese Patent Application Laid-Open No. 6-104223 discloses a method in which after processing using oxygen and nitrogen, a further processing is effected using oxygen and SF4. Moreover, Japanese Patent Application Laid-Open No. 5-160022 discloses a method in which a photoresist is ashed with an oxygen plasma, and a residue is then ashed with a hydrogen plasma.
However, in the case where a modified layer generated by ion implantation is removed with a hydrogen plasma or steam plasma, the processing efficiency generally becomes small due to its low reaction rate. Moreover, it is necessary to sufficiently raise the temperature of an article to be processed (hereinafter referred to as xe2x80x9cprocessing articlexe2x80x9d) in order to increase the reaction rate, so that the popping phenomenon is apt to take place more easily.
In a processing with a plasma of a mixed gas formed by adding to oxygen a gas containing fluorine as a halogen which is an example of the gas containing halogen, the processing efficiency is improved by the function of generated fluorine ions and fluorine radicals, compared with the case of using an oxygen plasma only. However, since low temperature processing is apt to give rise to a photoresist residue, in order to avoid this, it is necessary to effect processing at a high temperature which is apt to cause the popping.
In view of the problems as described above, in the actual producing process, after ashing with oxygen has been effected, oxides of a dopant remaining on a wafer as a processing article are cleaned and removed in a subsequent wet processing.
An object of the present invention is to provide a processing method that can remove a foreign matter on a surface of a processing article at a high efficiency without leaving any residue such as an oxide of an ion implanted dopant.
According to a first aspect of the present invention, there is provided a method of removing a residue comprising ashing and removing a dopant-implanted photoresist to expose a surface of a processing article and then removing a dopant-containing residue of the photoresist remaining on the surface of the processing article,
wherein the dopant-containing residue is removed at a temperature higher than the temperature at which the photoresist is ashed and removed.
According to a second aspect of the present invention, there is provided a method of processing an article comprising the steps of:
ashing and removing a dopant-implanted photoresist on a surface of an article at a first temperature; and
removing a dopant-containing residue of the photoresist at a second temperature higher than the first temperature.
According to a third aspect of the present invention, there is provided a method of producing a semiconductor device comprising the steps of:
forming a photoresist pattern on a surface of a substrate;
implanting a dopant in the substrate using the photoresist pattern as a mask;
ashing and removing a dopant-implanted photoresist on the surface of the substrate at a first temperature; and
removing a dopant-containing residue of the photoresist at a second temperature higher than the first temperature.